At a photolithography step upon production of a semiconductor device, photoresist is coated on the front surface of a semiconductor wafer (hereinafter referred to as “wafer”). Thereafter, a mask pattern is exposed on the resist and developed. As a result, a resist pattern is formed on the front surface of the wafer.
At such a photolithography step, the developing process is performed by for example a paddle method or a dip method. In the paddle method, developing solution is supplied to a wafer. On the other hand, in the dip method, a wafer is dipped in developing solution. In the state, the developing process is promoted. Thereafter, rinsing solution such as pure water as washing solution is supplied onto the wafer so as to wash away the developing solution. Finally, a drying process for blowing air to the wafer or rotating the wafer is performed so as to remove the rinsing solution from the wafer.
When the resist is for example negative type, a light-exposed portion is hardened. Thus, a non-hardened portion, namely a dissolvable portion of the resist, is dissolved with the developing solution. In contrast, when the resist is for example positive type, the light-exposed portion is dissolved with the developing solution.
Next, how for example negative type resist is developed will be described. As shown in FIG. 34, developing solution is applied onto resist 210 coated on the front surface of for example a wafer W for which an exposing process has been performed. Thereafter, the wafer W is kept for a predetermined time period. A dissolvable portion 211 dissolves in the developing solution. Thereafter, washing solution is supplied onto the front surface of the wafer W so as to wash away the developing solution from the wafer W. Thereafter, the wafer W is dried. As a result, a resist pattern 212 is obtained.
As shown in FIG. 35(a), the wafer for which the exposing process has been performed is held in a nearly horizontal position. Thereafter, the wafer W is placed on a spin chuck 213 that is rotatable around the vertical axis. In this state, the developing process is performed. First of all, developing solution D is coated on the entire front surface of the wafer W. Thereafter, the wafer W is stationary-developed for a predetermined time period, for example 60 seconds, so as to promote the developing reaction. After the predetermined time period has elapsed, as shown in FIG. 35(b), washing solution R such as pure water is supplied from a washing solution nozzle 214 that faces for example a center portion of the front surface of the wafer. In addition, the wafer W is rotated at a peripheral velocity of around 1000 rpm. With an action of centrifugal force, the developing solution D that contains a resist dissolvable component is washed away. Finally, as shown in FIG. 35(c), the wafer W is rotated at high speed so as to dry it.
However, since the size of the wafer W is becoming large in recent years, in the conventional method of which the wafer W is rotated and with an action of centrifugal force the developing solution D is washed away from the wafer W, the difference between the centrifugal force that acts at a periphery portion of the wafer W and the centrifugal force that acts at a center portion of the wafer W is large. Thus, the center portion at which the centrifugal force is weak may be insufficiently washed. In other words, the dissolvable component of the resist at a valley portion of the resist pattern has a high concentration and contains deposit of a resist component that has been dissolved, undissolved resist particles, and so forth. In other words, the dissolvable component may be in so-called muddy state. When the centrifugal force is low, frictional force of the deposit against for example the front surface of the wafer W and the wall surface of the resist pattern more strongly acts than the centrifugal force. As a result, even if the wafer W is rotated, the deposit may not be shaken off, but left. If the wafer W is dried with the deposit that adheres on the front surface of the pattern (the front surface of the resist or the front surface of the base material), there is a possibility of which a development defect takes place.
On the other hand, a method for strengthening the centrifugal force at the center portion of the wafer W with an increased number of rotations thereof has been studies. However, in this method, since the centrifugal force at the periphery portion of the wafer W is too strong, there is a possibility of which a resist pattern thereon peels off or collapses.
Moreover, in recent years, semiconductor devices are further becoming miniaturized. A resist pattern that is finely structured and that has a high aspect ratio has come out. Since a resist pattern is finely structure and has a high aspect ratio, when rinsing solution passes through patterns, surface tension of the rinsing solution causes pulling force to take place between the patterns. So-called a problem of “pattern collapse” takes place. As countermeasures against such a problem, a method of which the surface tension of rinsing solution is weakened with surfactant mixed with the rinsing solution is known. The method requires that the rinsing solution should be equally supplied onto the substrate. However, there is a problem of which the rinsing solution is not equally replaced with the developing solution.
If surfactant contains impurities such as particles, when the rinsing solution that contains the surfactant is supplied onto the substrate, there is a possibility of which a product defect takes place.